The most frequently used methods for repeated completion of production formations are as follows: gun-fire perforation, cumulative perforation, drilling and abrasive jet perforation, as well as hydraulic fracturing of formation (Enhancement of primary and repeated oil formations' completion quality/N. A. Petrov, V. G. Sultanov, I. N. Davydova, G. V. Konesev; under the editorship of Professor G. V. Konesev. St. Petersburg, Nedra LLC, 2007, p. 548).
Nowadays cumulative perforation is the most common because it can be quite easily implemented under any conditions. Though, this easiness in implementation does not mean the best efficiency. Thus, gun-fire perforation, cumulative perforation, drilling and abrasive jet perforation belong to point-type, i.e. completion of the formation takes place in a point (in a projection onto well wall) and to enhance connection quality it is necessary to perform multiple completion of a formation by this method.
The next level as per the quality of the completion is a kind of abrasive jet perforation—slot-type abrasive jet perforation, which performs formation completion in a plane (vertical or horizontal). This kind of formations' completion is the most gentle related to cement stone of the well and provides good connection with the formation as it allows obtaining clean channels (Development of technical support and methods of hydro-mechanical slot-type perforation process control. Author's abstract of dissertation in support for scientific degree of Candidate of Technical Sciences (Ph.D. in Technical Sciences). S. V. Nazarov, 2005). There are many variants of this kind of repeated formations' completion combining both mechanical completion of production string with blades, rollers and fully hydraulic completion of a string and cutting of filtration channel and slot. Disadvantage of this method is obtaining of well connection with formation only in one, two or three vertical planes (depending on number of nozzles).
Currently the method of repeated formation completion allowing obtaining maximal hydrodynamic connection between the formation and the well is hydraulic fracturing of formation (see e.g., RU 2485296). This technology became very commonly used due to its high efficiency, but it, as well as slot-type abrasive jet perforation, makes formation completion plane directional (vertical or horizontal). Also this technology has limitations of applicability under complicated mining and geological conditions (presence of gas caps or active bottom waters), as the crack of hydraulic fracturing has long vertical length and can extend beyond the production formation. Thus, the main disadvantage of this technology is essential availability of thick aquicludes (e.g., aquifuges) in the well between the production formation and other water or gas-bearing formations, which would prevent fracturing cracks from propagating to other formations.
The technology of slot hydraulic formation cutting was taken as the basis for implementation of the technology of hydrodynamic connection quality maximization, as this technology allows working under complicated mining and geological conditions and has the potential for improvement.
There is great variety of slot forming methods lately existing in this field, but almost all of them are limited to cutting vertical slots either under continuous mode (see. e.g., RU Patent 2282714), or under periodic mode with joining the slots in formation (see e.g., RU Patent 2365742).
The methods of production formations' completion by slot perforation are also widely known (see, e.g., RU Patent 2397317), when the perforator runs into the well down to the given depth with the subsequent moving of the perforator upwards and cutting a slot in the wall of the casing string/production string with removable disc cutter. Perforation is done in the well section by slot-type areas located relative to each other with a preset pitch along the spiral line around the axis of a string.
Making a slot on each area is done by moving the cutter axis in the plane of slot making as per the preset trajectory with simultaneous reciprocating movement of the perforator in vertical direction relative to casing string. The speed of perforator movement is selected based on design conditions of the production formation completion. Disadvantages of this method include the limitation of perforation height and depth by the length of disc cutter travel.
RU Patent 2393341 titled “Hydro-mechanical Slot Perforator” discloses a method for volumetric well perforation and proposes to install threading rollers of the perforator at an angle to the vertical axis for obtaining screw slots. The purpose of this method was creation of such slots that allow the casing string to withstand horizontal rock constituent to prevent the string from crushing. Eventually, the patent discloses that the device allows well equipping with the system of extended crosswise channels. However, the disclosed methods have multiple disadvantages, including availability of channels; specifically slots' creation instead of thorough removal of the mine rocks in the area of contact, i.e., formation completion takes place along the helicoid surface and in an involute it is a planar variant, which leads to appearance of additional filtration resistances during filtration of the fluids from the formation into the well.